Bitter war over Rinehart family billion-dollar empire far from over

Gina Rinehart's two eldest children began new legal action today to reclaim a huge portion of the family trust, saying their mining magnate mother stole it from them.

Bianca Rinehart and John Hancock may have won control of the family trust but their lawyers claimed today their mother had transferred significant assets from it in a way that was "wholly fraudulent" and that she "stole from her children" and concealed the true facts in a "demonstration of a guilty mind".

Bianca Rinehart and John Hancock are fighting their mother in court. (9NEWS) ()

Lawyer Christopher Withers claimed that, following the death of her father, Mrs Rinehart de-valued the Hancock Family Memorial Foundation from $61 million to a hugely under-valued minus $27 million and then used that diminished value to increase her share in the company.

He said Lang Hancock had intended the children to own 49 percent of the business and Mrs Rinehart 51 percent, but instead they own 24 percent to their mother's 76 percent.

Lawyers claim Ms Rinehart de-valued the family trust to increase her share in the company. (9NEWS) ()Bianca and John's lawyer said Lang Hancock intended for his grandchildren to own 49 percent of the business, with the remaining 51 percent for daughter Gina. (9NEWS) ()

Mrs Rinehart's children admitted that while they had signed away the right to the assets, they were young and their mother used influence and misled them, and forced them to sign in "truly awful circumstances".

Bianca Rinehart said she was "threatened" and felt her "career and livelihood were on the line" and after she signed she was "crying and distraught".

In a statement, Hancock Prospecting said the accusations made in court would be disputed and that they are false and will be strongly defended.